# 正五角形面积
# 面积计算公式(正五角形边长为s),则 ares = 5*s^2/4*tan(pi/5)

# 导入数学模块math
import math

# 输入正五角形边长
s = eval(input("Input the length of the side of a regular pentagon:"))

# 分子
Molecule = 5 * s ** 2

# 分母
Denominator = 4 * math.tan(math.pi / 5)

area = Molecule / Denominator
print(f"The area of the triangle is : {area}")
